1. Field of the Invention The present invention relates to a laser build-up method and relates to, for example, a laser build-up method for a valve seat.
2. Description of Related Art
It is required for a valve seat of a cylinder head which a valve repeatedly contacts under a high-temperature environment to have a high heat resistance and a high wear resistance. Therefore, the valve seat is obtained by forming an annular counter sunk groove by machine processing on an edge of an opening end of an inlet/outlet port of a cylinder head roughly formed material and forming a cladding layer made of copper-based alloy or the like in the counter sunk groove.
As the build-up method for the valve seat, a laser build-up method (a so-called laser cladding method) that irradiates a laser beam while a metallic powder is being supplied to a counter sunk groove to form a cladding layer is known. It is known in this laser build-up method that blow holes tend to occur in an overlapped part in which a starting end part and a terminating end part of the cladding layer overlap each other.
In order to reduce the blow holes, Japanese Unexamined Patent Application Publication No. 2010-201480 discloses a laser build-up method in which an output of a laser is increased to a predetermined amount, the terminating end part of the cladding layer is then formed, and the terminating end part is overlapped with the starting end part.
The present inventors have found that blow holes are generated in the overlapped part when the state of excess metallic powder (excess powder) deposited in the starting end part of the cladding layer becomes a semi-molten one since a laser beam comes close to it, the excess metallic powder becomes balls, and then the balls are absorbed in a melt pool. Even when the output of the laser is increased in the overlapped part as disclosed in the method disclosed in Japanese Unexamined Patent Application Publication No. 2010-201480, it is impossible to decrease an excess powder, which causes the occurrence of the blow holes in the overlapped part.
The present inventors have found that it is possible to suppress the occurrence of the blow holes by increasing the flow rate of the seal gas sprayed onto the melt pool and removing the excess powder deposited in the starting end part.
However, the simple increase in the flow rate of the seal gas results in a decrease in the yield of the metallic powder.
The present invention has been made in order to solve the aforementioned problem and aims to provide a laser build-up method capable of improving the yield of the metallic powder while suppressing the occurrence of the blow holes in the overlapped part.